1. Field of the Invention
This invention relates to chain tensioners, and particularly a chain tensioning device for chain drives, such as used on motorcycles.
2. Description of the Prior Art
There has been a continuing problem created by the slack required to be provided in the chain drive of motorcycles. The slack is required because the distance between the motor drive sprocket and the wheel sprocket varies depending upon the displacement of the shock absorbers which extend between the rear wheel mounting or swing frame and the base frame on which the motor housing is secured. The existence of such slack in the chain drive results in frequent derailment of the chain from the wheel or motor sprocket which, if it occurs at high speed, can cause considerable damage to the motor, the sprocket, the frame and the rider. Attempts to control the chain under high speed operating conditions have been largely unsuccessful. For instance, U.S. Pat. No. 1,962,223 teaches the use of a tensioning mechanism in conjunction with a chain, however it is applicable to only one reach of the chain, whereas slack appears in both reaches of the chain under certain circumstances.
U.S. Pat. No. 3,448,628 relates to a device for tensioning the driving chain in a bicycle equipped with a coaster break. The necessity for a tensioning device results from the fact that as the chain shifts from one larger gear to a smaller gear the excess length of chain appearing in the lower reach of the chain must be taken up in some way. This patent teaches independent mechanisms for taking up the slack in the upper and lower reaches of a bicycle chain.
Krause U.S. Pat. No. 3,575,058 teaches the use of independent devices for tensioning the upper and lower reaches of a chain drive, the devices including a bracket adapted to be mounted on a fixed object such as a wall and projecting over the upper and lower reaches of the chain in such a way that rollers mounted on the bracket come in contact with the upper and lower reaches of the chain. This construction is primarily useful for the drive mechanisms for equipment that is fixed in place and does not appear to be applicable for mobile or motorcycle drive chains.
U.S. Pat. No. 3,677,103 also relates to a tensioning device for bicycle chains but does not teach the concept of a device operating in conjunction with both upper and lower reaches of such chains.
U.S. Pat. No. 3,785,219 relates to a device for tensioning the upper reach of a bicycle chain when the main drive sprocket is rotated in reverse to operate a coaster break. This patent does not teach the concept of a single device engaging both upper and lower reaches of the chain to accomodate slack in the chain.
U.S. Pat. No. 3,913,410 relates to a tensioning mechanism for a variable speed sprocket and chain drive assembly in which two parallel chains are driven by (or drive) a variable diameter sprocket. Spring pressed idler rollers are provided independently associated with each reach of the chain to accommodate slack in the chain when the effective diameter of the sprocket is reduced.
U.S. Pat. No. 3,463,022 also relates to a chain tensioning device, however, it utilizes hydraulics to control the slack in only one reach of the chain.
From the foregoing it will be apparent that the problems created by slack in a chain drive have been in existence for a long time. It is also apparent and surprising that no one has considered the possibility of combining in one single mechanism means for controlling the slack in both reaches of a motorcycle chain under all operating conditions. Accordingly, it is one of the principal objects of this invention to satisfy that need.
So far as is known, the relationship between the rotational axis of the rear wheel sprocket assembly of a motorcycle and the rotational axis of the motor drive sprocket is a variable one for the reason that the swing frame member on which the rear wheel is mounted is pivoted about an axis spaced from the axis of rotation of the motor drive sprocket so that the distance between the rotational axis of the wheel sprocket and the rotational axis of the motor drive sprocket varies in relation to the displacement of the rear wheel or swing frame assembly in relation to the main frame as permitted by the shock absorbors. Such variation in the distance between the rotational axes of the sprockets causes variation in the amount of slack in both the upper and lower reaches of the chain, again depending upon the degree and direction of displacement of the rear wheel in relation to the main frame as permitted by the shock absorbers. Accordingly, it is one of the principal objects of the present invention to provide a chain tensioning device that may be easily mounted on the swing frame member and which will control the slack in both reaches of the chain through all of its variations.
During the operation of a motorcycle, different slack conditions in the chain are created by different modes of operating the motorcycle. For instance, when the motorcycle is under power and is being driven by the motor, the top reach of the chain is generally taut between the upper peripheries of the motor drive and wheel sprockets, while the lower reach of the chain contains all of the slack. Accordingly, it is another object of this invention to provide a single chain tensioning device applicable to both upper and lower reaches of the chain which will accomodate all of the slack that is transferred to the lower reach of the chain when the motorcycle is being driven by the motor.
Under a different circumstance, e.g., when the motorcycle is driving the motor, the lower reach of the chain will be taut between the lower peripheries of the motor drive and wheel sprockets while the upper reach of the chain will contain all of the slack. With the motorcycle traveling at high speed, and the chain rotating rapidly under these conditions, there is a tendency for the chain to be derailed from the motor drive sprocket because of the large amount of slack. Accordingly, still another object of the invention is to provide a single chain tensioning device that will accommodate the transfer of slack from the lower reach of the chain to the upper reach of the chain under these conditions and which will keep sufficient tension on the upper reach of the chain to prevent its being inadvertently disengaged.
When a motorcycle is being operated in rough terrain, such as on dirt trails, it is normal operating procedure to accelerate and decelerate suddenly so that the transfer of slack between the upper and lower reaches of the chain will occur frequently and with suddenness on a single ride. Additionally, because of rough terrain and the necessity to lean the motorcycle precariously going around sharp curves or bends in trails, because of the large amount of slack in the chain, there is a tendency for the chain reaches to shift laterlly, thus causing derailment from the sprockets on which it is mounted. In other words, there is a tendency for the chain to be displaced laterally out of the plane of the sprockets. Accordingly, still another object of the present invention is to provide a single device capable of being attached to a frame member of the motorcycle in association with the chain drive and which will engage both reaches of the chain and prevent such lateral displacement of the chain out of the plane of the sprockets while simultaneously controlling the tension on the chain.
Because of the necessity of having a great deal of slack in the chain, there is a tendency for the motorcycle to respond slugishly to the throttle. Accordingly, it is another object of the present invention to provide a device that controls the tension in both reaches of the chain so as to improve throttle response.
It has been found that when acceleration and deceleration occur rapidly, such as in a race or on a trail, excessive slack in the chain creates a considerable amount of drive line shock. Accordingly, another object of the invention is to provide a device easily attachable to a frame member of the motorcycle and which is operative to control tension in both reaches of the chain as to eliminate or materially diminish drive line shock.
The invention possesses other objects and features of advantage, some of which, with the foregoing, will be apparent from the following description and the drawings. It is to be understood however that the invention is not limited to the embodiment illustrated and described since it may be embodied in various forms within the scope to the appended claims.